Hi All,
Having a problem doing a flow deform spiral - have included 3dm file have tried positioning the non deformed shape in various positions around the control curve. But keep getting a crossover in the final deform pattern. Any words of wisdom appreciated.

thanks
Alex.

Hi Alex, is it because you've got the base line positioned off a little bit to the side of the object rather than running right down the center of it?

- Michael

I experimented with the objects and flow for a while.

The red line is not quite parallel with the center axis of the object.

EDIT: The next sentence is false:
Using a center axis does not seem to make any difference to the Flow, as far as I can tell.

After trimming the external parts of a new center axis, as well as trimming the target curve,
Flow begins the flowed object parallel to the xy plane, but then twists the flowed object in excess of 90 degrees.

I wonder what the rotation frame of the spiral target curve is, and if there is another way to form the target curve, with "horizontal" rotation frame?

- Brian

How about twisting the initial object, in excess of 90 degrees, +90+, or -90+, before the flow?

Can the MoI properties of tangents and derivatives, etc., of a curve be used to investigate the rotation frame(s) of the spiral target curve?

Hi Brian,

re:
> Can the MoI properties of tangents and derivatives, etc., of a curve be used to investigate the
> rotation frame(s) of the spiral target curve?

Not quite, the rotation of a sweep frame is another thing, look up "Bishop Frame" for references.

Bishop, R. L. "There is more than one way to frame a curve.",
American Mathematical Monthly (1975) pp. 245-251

The intrinsic "Frenet frame" of the curve formed by the tangent and curvature vectors does not work well using it for sweep frame rotation.

- Michael

Hi Brian,

re:
> Using a center axis does not seem to make any difference to the Flow, as far as I can tell.

For me it does, I get the red result from the original setup, and the blue result from one
where I moved the base line to run down the center of the object:



- Michael

Thank you Michael.
(I added an edit to indicate that my statement was false, re non-center axis base curve.)

-Brian
(I have heard about Bishop frames. Will have to study Bishop frames for spiral... I guess Flow must use them internally.)

Hi Brian, yes curve-to-curve Flow uses the Bishop frames that is also used by Sweep.

I would like to add a way to control the start normal on the base and the start normal on the target curve.

- Michael

Thanks Michael, Brian indeed the centreline is AOK I though I tried that early in the experiments cycle the ol keep it simple stupid method always wins.

Alex.